Currently, electrophotographic image-forming apparatuses are regarded as the constitution which is most suitable for meeting requirements for the high-speed production of quality images, and bearing of small dimensions for optimizing use of space saving in an office.
In recent years, in high demand have been output apparatuses for computers or output apparatuses capable of performing various image processing. Specifically, these are laser beam printers (hereinafter referred to as LBP) or digital copiers.
The photoreceptors which can be employed in such apparatuses are required to exhibit sufficient sensitivity for long wavelength radiation generated by light sources such as semiconductor lasers and the like. Therefore, recently, phthalocyanine compounds have received much attention as a charge generating material (abbreviated as "CGM") having a high sensitivity even in the long wavelength region. The phthalocyanine compounds are classified into two main categories, that is, metallic phthalocyanines and nonmetallic phthalocyanines and a variety of compounds have been proposed. Of those, titanylphthalocyanines (hereinafter referred to as "TiOPc") have received considerable attention as the CGM from which can be realized high sensitivity and quality images. The TiOPc exhibits sufficient sensitivity in the long wavelength region, specifically the range between 600 and 850 nm (hereinafter, the term "long wavelength region" will refer to this wavelength region). Therefore, the TiOPc is a markedly suitable material for preparing the photoreceptor for the image-forming apparatus comprising a light source having the maximum radiation energy in this wavelength region such as semiconductor laser, LED, EL (electroluminescence), LCD (liquid crystal shutter), etc.
However, as the resolution of images is improved, there have been problems with grained interference fringes (Moire image). As to the reason for these problems, when an exposure light source is coherent light of a long wavelength, the light is not totally absorbed by a photosensitive layer, and the transmitted light is subjected to regular reflection from the support surface. As a result, multipath reflection of the light of the laser beam is generated in the photosensitive layer, and it is assumed that interference is caused between the multipath reflected light and reflected light from the surface of the photosensitive layer.
In order to eliminate this phenomenon, a method is employed in which the electrically conductive surface of a support is intentionally roughened and the formation of interference is prevented by scattering the light transmitted through the photosensitive layer. However, when the surface is excessively roughened, traces from processing the support appear in the image. On the other hand, when the surface roughness is not enough, a Moire pattern is generated. It has been difficult to maintain uniform and appropriate roughness on the surface of the support in the production process.
The photoreceptor is basically composed of an electrically conductive support and a photosensitive layer. However, in order to improve the adhesion of the support to the photosensitive layer, to prevent image defects caused by the charge injection from the electrically conductive support, to improve charging properties of the photoreceptor, and the like, in many cases, a sublayer is provided between the electrically conductive support and the photosensitive layer.
Particularly, in the reversal development process employed in a laser printer, image defects such as micro black points known as black spots (in the case of normal development, white spots on the solid black image), transfer memory, etc. are frequently generated. In order to minimize such image defects, a sublayer (occasionally termed an interlayer) having better quality, has been desired. As the sublayer, for example, a resin layer comprising a polyamide resin, a polyester resin, a polyurethane resin is listed and is most generally employed.
When such a sublayer, composed of a resin layer, is employed in combination with an imidazoleperylene compound or TiOPc, images excellent in contrast and resolution are obtained even though the resulting combination is employed in a high speed machine. However, such excellent quality is obtained only when employed under environmental conditions such as normal temperature and humidity and is only obtained during an initial period. When employed under specific environmental conditions such as high temperature and humidity or low temperature and humidity, or for the continuous production of a number of copies, several problems are caused.
For example, at high temperature and humidity, the resistance of the resin layer increases and the barrier properties increase. As a result, problems are caused such that the sensitivity decreases and after repeated use, the residual electric potential increases. Particularly, when TiOPc is employed as a CGM, the charge generating capability of TiOPc may be degraded and the above-mentioned problems are markedly increased.
As shown above, when the imidazoleperylene compound or TiOPc is employed in combination with the resin layer as a sublayer, some advantages are achieved. On the contrary, however, major problems such as formation of white spots (or black spots), deterioration of electric potential characteristics, etc. are caused.
As a means to solve those problems, Japanese Patent Publication Open to Public Inspection No. 58-93062 discloses the formation of a sublayer by mixing a resin with a metal alkoxide compound or an organic metal compound, and furthermore, a technique for the formation of a sublayer employing an organic metal compound or a silane coupling agent, without the use of a resin.
For example, in Japanese Patent Publication Open to Public Inspection No. 62-272277, metal alkoxide compounds and silane coupling agents are employed. Furthermore, in Japanese Patent Publication Open to Public Inspection Nos. 3-73962, 4-36758, etc., a zirconium chelating compound and a silane coupling agent are employed in combination.
In the electrophotographic photoreceptor in which writing is performed with a laser beam, a grained image defect (Moire pattern) is formed by the interference of a laser beam caused by unevenness in the thickness of the photoreceptor layer. The defect is markedly generated when an organic metal series sublayer is employed which exhibits a larger reflection ratio, which is thicker than that composed of a resin. As a method to prevent such problems, for example, it is has been shown that if the surface of a support is intentionally roughened, the generation of interference light is prevented by scattering the incident light. However, the prevention is not complete. Furthermore, when the surface is excessively roughened, an uneven surface is formed on the photosensitive layer and troubles such as poor cleaning result.